The use of distributed computing systems, e.g., “cloud computing,” has become increasingly common for consumers and enterprises, especially for data storage. This so-called “cloud data storage” employs large numbers of networked storage servers that are organized as a unified repository for data, and are configured as banks or arrays of magnetic hard disk drives (HDDs) and/or solid-state drives (SSDs). Typically, these servers are arranged in high-density configurations to facilitate such large-scale operation. For example, a single cloud data storage system may include thousands or tens of thousands of storage servers installed in stacked or rack-mounted arrays.
The majority of storage in cloud data storage systems is provided by HDDs, due to the low cost-to-capacity associated with such drives. To further increase the storage density of HDDs, shingled magnetic recording (SMR) has been introduced. While conventional HDDs record data by writing to non-overlapping magnetic tracks that are parallel to each other, drives using SMR write to a new track that overlaps a portion of the previously written track, so that the tracks partially overlap like roof shingles. Thus, SMR produces tracks that are narrower, allowing for higher track density and increased overall per-drive storage capacity.
However, the overlapping-tracks written using SMR greatly slows the writing of randomly located data, adding unwanted latency in any storage system that uses SMR drives. Because writing to one track overwrites an adjacent track, data can only be written sequentially to a particular group of overlapping tracks, known in the art as a “band,” which is different than the normal random access behavior of traditional HDDs. To write new data to a specific location within a such a band, the entire band is read and then rewritten with the new data written in the specific location. Thus, the implementation of randomly located write commands in an SMR drive can be time-consuming and produce significant write amplification. Because latency is a critical performance parameter of cloud data storage systems, the use of SMR drives in such data storage systems can be problematic.